Nonaqueous electrolyte battery, battery pack and vehicle

ABSTRACT

A nonaqueous electrolyte battery includes a positive electrode, a negative electrode and a nonaqueous electrolyte. The negative electrode contains a lithium compound and a negative electrode current collector supporting the lithium compound. A log differential intrusion curve obtained when a pore size diameter of the negative electrode is measured by mercury porosimetry has a peak in a pore size diameter range of 0.03 to 0.2 μm and attenuates with a decrease in pore size diameter from an apex of the peak. A specific surface area (excluding a weight of the negative electrode current collector) of pores of the negative electrode found by mercury porosimetry is 6 to 100 m 2 /g. A ratio of a volume of pores having a pore size diameter of 0.05 μm or less to a total pore volume is 20% or more.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2007-085716, filed Mar. 28, 2007,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nonaqueous electrolyte battery, and abattery pack and a vehicle provided with this nonaqueous electrolytebattery.

2. Description of the Related Art

As shown in JP-A 5-151953 (KOKAI) and JP-A 2006-59690 (KOKAI), it isknown that an improvement in the performance of a battery can beattained by knowing the state of particles in the battery electrodebased on the measurement of the pore distribution of the batteryelectrode by using mercury porosimetry. In this case, JP-A 5-151953(KOKAI) relates to an invention using, as the negative electrode activematerial, a mixture of a metal oxide and an insoluble and infusible baseof a polyacene type skeleton structure having a specific surface area of600 m²/g or more as measured by a BET method. On the other hand, JP-A2006-59690 (KOKAI) relates to an invention using, as the negativeelectrode active material, a composite graphite material having arelatively small specific surface area of 1.5 to 5 m²/g as measured by aBET method.

When a lithium compound having a small ionic diffusibility in a solid isused as the negative electrode active material, it is difficult todevelop a high power battery. However, it is known that high power canbe attained by using microparticles of this lithium compound. Thesemicroparticles of a lithium compound pose the problem that they cause alarge variation in the output characteristics of a battery depending onthe production method of the battery, because they have thecharacteristic that they tend to be coagulated in a process of producingan electrode using these microparticles.

The nonaqueous electrolyte battery described in JP-A 2007-18882 (KOKAI)uses, as the negative electrode active material, lithium compoundparticles having a lithium ion absorption potential of 0.4V (vs. Li/Li⁺)or more and an average particle diameter of 1 μm or less. In JP-A2007-18882 (KOKAI), during the manufacture of a negative electrode, aslurry is stirred strongly in a specified condition to reducecoagulation among lithium compound particles. It is described in JP-A2007-18882 (KOKAI) that the edges of lithium compound particles arescraped away by this stirring to smooth the surfaces of these particles.JP-A 2007-18882 (KOKAI) also describes that, as a result, these lithiumcompound particles can be filled at a high density in a negativeelectrode. Therefore, the pore size diameter distribution is shifted tothe smaller pore size diameter side, with the result that a first peakhaving a mode diameter of 0.01 to 0.2 μm and a second peak having a modediameter of 0.003 to 0.02 μm appear in the log differential intrusioncurve of the negative electrode, as measured using mercury porosimetry.JP-A 2007-18882 (KOKAI) describes that the cycle life of a nonaqueouselectrolyte battery is improved by specifying the pore volume in eachpeak range.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda nonaqueous electrolyte battery, comprising:

a positive electrode;

a negative electrode containing a lithium compound and a negativeelectrode current collector supporting the lithium compound; and

a nonaqueous electrolyte,

wherein a log differential intrusion curve obtained when a pore sizediameter of the negative electrode is measured by mercury porosimetryhas a peak in a pore size diameter range of 0.03 to 0.2 μm andattenuates with a decrease in pore size diameter from an apex of thepeak,

a specific surface area (excluding a weight of the negative electrodecurrent collector) of pores of the negative electrode found by mercuryporosimetry is 6 to 100 m²/g, and

a ratio of a volume of pores having a pore size diameter of 0.05 μm orless to a total pore volume is 20% or more.

According to a second aspect of the present invention, there is provideda battery pack comprising a nonaqueous electrolyte battery, thenonaqueous electrolyte battery comprising:

a positive electrode;

a negative electrode containing a lithium compound and a negativeelectrode current collector supporting the lithium compound; and

a nonaqueous electrolyte,

wherein a log differential intrusion curve obtained when a pore sizediameter of the negative electrode is measured by mercury porosimetryhas a peak in a pore size diameter range of 0.03 to 0.2 μm andattenuates with a decrease in pore size diameter from an apex of thepeak,

a specific surface area (excluding a weight of the negative electrodecurrent collector) of pores of the negative electrode found by mercuryporosimetry is 6 to 100 m²/g, and

a ratio of a volume of pores having a pore size diameter of 0.05 μm orless to a total pore volume is 20% or more.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a characteristic curve showing the pore size diameterdistribution of a negative electrode used in a nonaqueous electrolytebattery according to a first embodiment when the pore size diameterdistribution is measured using mercury porosimetry;

FIG. 2 is a partially broken perspective view showing a nonaqueouselectrolyte battery according to the first embodiment;

FIG. 3 is a partially broken perspective view showing another nonaqueouselectrolyte battery according to the first embodiment;

FIG. 4 is a pattern diagram of an enlarged section of the part shown byA in the nonaqueous electrolyte battery shown in FIG. 3;

FIG. 5 is a perspective view showing a typical electrode group having alaminate structure used in a nonaqueous electrolyte battery according tothe first embodiment;

FIG. 6 is a partially broken perspective view showing a nonaqueouselectrolyte battery according to the first embodiment;

FIG. 7 is an explosion perspective view of a battery pack according to asecond embodiment;

FIG. 8 is a block diagram showing an electric circuit of a battery packshown in FIG. 7;

FIG. 9 is a pattern diagram showing a series hybrid car according to athird embodiment;

FIG. 10 is a pattern diagram showing a parallel hybrid car according tothe third embodiment;

FIG. 11 is a pattern diagram showing a series-parallel hybrid caraccording to the third embodiment;

FIG. 12 is a pattern diagram showing a car according to the thirdembodiment;

FIG. 13 is a pattern diagram showing a hybrid motorcycle according tothe third embodiment;

FIG. 14 is a pattern diagram showing an electric motorcycle according tothe third embodiment;

FIG. 15 is a pattern diagram showing a rechargeable vacuum cleaneraccording to a fourth embodiment; and

FIG. 16 is a structural view of a rechargeable vacuum cleaner accordingto FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION

The inventors of the present invention have made earnest studies toimprove the output performance of a nonaqueous electrolyte battery usinga lithium compound as the negative electrode active material and as aresult, found that a high output performance is obtained when the poresize diameter distribution of the negative electrode as measured usingmercury porosimetry satisfies the following conditions (1) to (4).

(1) The log differential intrusion curve of the negative electrodemeasured using mercury porosimetry has a peak in a pore size diameterrange of 0.03 μm to 0.2 μm.

(2) The above log differential intrusion curve attenuates with adecrease in pore size diameter from the apex of the above peak.

(3) The specific surface area of pores measured using the above mercuryporosimetry is 6 m²/g or more and 100 m²/g or less. In this case, theweight of the negative electrode which is used to calculate the specificsurface area of pores is a value excluding the weight of the negativeelectrode current collector.

(4) The ratio of the volume of pores having a pore size diameter of 0.05μm or less to the total pore volume is 20% or more. The above ratio isfound by mercury porosimetry.

A negative electrode which satisfies the above condition (3) is superiorin nonaqueous electrolyte impregnation ability. It is desirable to uselithium compound particles having a fine particle size to satisfy theabove condition (3). However, if the particle size of lithium compoundparticles is smaller, a flock tends to be produced in a process ofproducing the negative electrode. A negative electrode which satisfiesthe above conditions (1), (2) and (4) is reduced not only in the amountof this flock but also in the amount of broken pieces of primaryparticles of the lithium compound and therefore, the uniformity of thedistribution of a negative electrode active material can be improved.Therefore, because the nonaqueous electrolyte impregnation ability ofthe negative electrode and the uniformity of the distribution of thenegative electrode active material can be improved, the DC resistance ofthe negative electrode is reduced and therefore, the output performanceof the nonaqueous electrolyte battery is improved.

FIG. 1 shows an example of a distribution curve of pore volume of thenegative electrode which is measured by mercury porosimetry. In FIG. 1,the abscissa is the pore size diameter (radius), the right ordinate isthe log differential intrusion and the left ordinate is the cumulativeintrusion. The log differential intrusion curve is a curve expressed bythe right ordinate to show a variation in the log differential intrusionas a function of the pore size diameter. As shown in FIG. 1, a peakexists in a pore size diameter range of 0.03 μm to 0.2 μm. Also, thecurve attenuates with a decrease in pore size diameter from the apex. Inother words, no other peak is present at a pore size diameter smallerthan the pore size diameter of the apex of the peak. Here, thedescription “a peak exists in a pore size diameter range of 0.03 μm to0.2 μm” means that the mode diameter of the peak which is the pore sizediameter of the apex of the peak is 0.03 μm or more and 0.2 μm or less.The pore size diameter is more preferably 0.04 μm or more and 0.1 μm orless.

The curve defined by the left ordinate indicates the integrating volumeobtained by integrating the volumes of pores having a pore size diameterof 100 μm or less in the direction of a reduction in pore size diameter,that is, a cumulative intrusion. The maximum value V₁ of the cumulativeintrusion in the cumulative intrusion curve corresponds to the totalpore volume of the negative electrode. The volume of pores having poresize diameters of 0.05 μm or less is a difference between the maximumvalue V₁ (total pore volume) of the cumulative intrusion and thecumulative intrusion V₂ at a pore size diameter of 0.05 μm. The ratio ofthe volume of pores having a pore size diameter of 0.05 μm or less tothe total pore volume is preferably 20% or more and more preferably 30%or more. Also, the upper limit of the ratio may be designed to be 90%.The reason for this is because if a negative electrode is used which isprovided with pores mostly having a small diameter, as in the case wherethe ratio of pores having a pore size diameter of 0.05 μm or lessexceeds 90%, there is a concern that the negative electrode activematerial detaches from the current collector metal foil because itbecomes less resistant to mechanical bending and to expansion andshrinkage thereof during charging and discharging.

If, among the above conditions (1), (2) and (4), any condition isunsatisfied, the negative electrode is greatly deteriorated in outputperformance because the uniformity in the distribution of a negativeelectrode active material in the negative electrode is reduced.

Further, the total pore volume is preferably in the range of 0.1 to 0.5mL/g per 1 g of the negative electrode, excluding the negative electrodecurrent collector. When the total pore volume is less than 0.1 mL/g,there is a concern that a high output performance is not obtainedbecause only an insufficient reaction field is obtained on the surfaceof the electrode. When the total pore volume is larger than 0.5 mL/g, onthe other hand, side reactions other than the battery reaction areeasily caused and there is therefore the possibility that a performanceobtained when a charge and discharge operation is repeated, that is, acycle performance is deteriorated. The total pore volume is morepreferably in the range of 0.11 mL/g or more and 0.4 mL/g or less.

The negative electrode is porous and comprises a negative electrodecurrent collector and a negative electrode active material-containinglayer which is supported on one or both surfaces of the currentcollector and contains an active material, a binder and as required, aconductor.

As the negative electrode active material, a lithium compound thatabsorbs and releases lithium ions is preferable. Examples of the lithiumcompound include lithium oxides, lithium sulfides and lithium nitrides.These compounds include compounds which contain no lithium in anuncharged state but contain lithium when they are charged.

Examples of these oxides include metal oxides containing titanium as themetal component, amorphous tin oxide such as SnB_(0.4)P_(0.6)O_(3.1),tin-silicon oxides such as SnSiO₃, silicon oxide such as SiO andtungsten oxides such as WO₃. Among these compounds, metal oxidescontaining titanium as the metal component are preferable.

Examples of the metal oxides containing titanium as the metal componentmay include lithium-titanium oxides and titanium-based oxides containingno lithium when synthesized. Examples of the lithium-titanium oxides mayinclude lithium titanate having a spinel structure and lithium titanatehaving a ramsdellite structure. Examples of lithium titanate having aspinel structure may include Li_(4+x)Ti₅O₁₂ (x varies in the range:−1≦x≦3, depending on a charge/discharge reaction). Examples of lithiumtitanate having a ramsdellite structure may include Li_(2+y)Ti₃O₇ (yvaries in the range: −1≦y≦3, depending on a charge/discharge reaction).Examples of the titanium-based oxides include TiO₂ and metal compositeoxides containing Ti and at least one element selected from the groupconsisting of P, V, Sn, Cu, Ni and Fe. TiO₂ is preferably of an anatasetype that is heat-treated at a temperature of 300 to 500° C. to provideit with low crystallinity. Examples of the metal composite oxidescontaining Ti and at least one element selected from the groupconsisting of P, V, Sn, Cu, Ni and Fe may include TiO₂—P₂O₅, TiO₂—V₂O₅,TiO₂—P₂O₅—SnO₂ and TiO₂—P₂O₅-MeO (Me is at least one element selectedfrom the group consisting of Cu, Ni and Fe). This metal composite oxidepreferably has low crystallinity and has a microstructure in which acrystal phase and an amorphous phase coexist or an amorphous phaseexists independently. When the metal composite oxide has such amicrostructure, the cycle performance can be greatly improved. Amongthese compounds, lithium-titanium oxide and metal composite oxidescontaining Ti and at least one element selected from the groupconsisting of P, V, Sn, Cu, Ni and Fe are preferable.

Examples of the sulfides include titanium sulfide such as TiS₂,molybdenum sulfide such as MoS₂ and iron sulfides such as FeS, FeS₂ andLixFeS₂ (0<x).

Examples of the nitrides include lithium-cobalt nitrides (for example,Li_(x)Co_(y)N, 0<x<4, 0<y<0.5).

The negative electrode active material preferably contains at least onetype selected from lithium titanate having a spinel structure, such asLi_(4+x)Ti₅O₁₂, FeS and FeS₂. And the negative electrode active materialis most preferably lithium titanate having a spinel structure. Becauselithium titanate having a spinel structure has excellent lithium-ionacceptability, a less resistant coating film can be formed on thesurface of the negative electrode by specifying initial chargeconditions.

Examples of the above conductive agent may include acetylene black,ketjen black, graphite and metal powder.

Examples of the binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), fluorine rubbers and styrene butadienerubber.

The compounding ratio of the above negative electrode active material,conductive agent and binder is preferably as follows: the negativeelectrode active material: 80 to 98% by weight, the conductive agent: 0to 20% by weight and the binder: 2 to 7% by weight.

It is desirable for the current collector of the negative electrode tobe formed of aluminum foil or aluminum alloy foil. It is also desirablefor the current collector to have an average crystal grain size notlarger than 50 μm. In this case, the mechanical strength of the currentcollector can be drastically increased so as to make it possible toincrease the density of the negative electrode by applying the pressingunder a high pressure to the negative electrode. As a result, thebattery capacity can be increased. Also, since it is possible to preventthe dissolution and corrosion deterioration of the current collector inan over-discharge cycle under an environment of a high temperature notlower than, for example, 40° C., it is possible to suppress theelevation in the impedance of the negative electrode. Further, it ispossible to improve the output performance, the rapid chargingperformance, and the charge-discharge cycle performance of the battery.It is more desirable for the average crystal grain size of the currentcollector to be not larger than 30 μm, furthermore desirably, not largerthan 5 μm.

The average crystal grain size can be obtained as follows. Specifically,the texture of the current collector surface is observed with anelectron microscope so as to obtain the number n of crystal grainspresent within an area of 1 mm×1 mm. Then, the average crystal grainarea S is obtained from the formula “S=1×10⁶/n (μm²)”, where n denotesthe number of crystal grains noted above. Further, the average crystalgrain size d (μm) is calculated from the area S by formula (A) givenbelow:d=2(S/π)^(1/2)  (A)

The average crystal grain size of the aluminum foil or the aluminumalloy foil can be complicatedly affected by many factors such as thecomposition of the material, the impurities, the process conditions, thehistory of the heat treatments and the heating conditions such as theannealing conditions, and the crystal grain size can be adjusted by anappropriate combination of the factors noted above during themanufacturing process.

It is desirable for the aluminum foil or the aluminum alloy foil to havea thickness not larger than 50 μm, more desirably not larger than 25 μm.Also, it is desirable for the aluminum foil to have a purity not lowerthan 99%. It is desirable for the aluminum alloy to contain anotherelement such as magnesium, zinc or silicon. On the other hand, it isdesirable for the amount of the transition metal such as iron, copper,nickel and chromium contained in the aluminum alloy to be not largerthan 1%.

A production method of the negative electrode will be explained. Thisnegative electrode is manufactured by suspending the negative electrodeactive material, conductive agent and binder in an appropriate solventand by applying this suspension to the current collector, followed bydrying and pressing to make a band-shaped material. The process ofpreparing the suspension is important. In a so-called kneading step inwhich the suspension is mixed in the condition of a low solvent ratio,the temperature is set to 5 to 10° C. during kneading to carry out thiskneading process under a small shearing force for a time as long as 12hours to 18 hours, whereby finer flocks are sufficiently pulverized.Moreover, the obtained suspension is circulated for 10 to 90 minutes byusing a beads mill with a vessel having a capacity of A [L] at a flowrate of A to 10 A [L/min] to make a suspension free from any flock. Atthis time, the diameter of the beads is preferably 0.01 mmφ or more and0.45 mmφ or less. When the suspension as the product to be treated ismade to pass through the beads mill using small-diameter beads at alarge flow rate, that is, when the retention time during which thesuspension is made to pass one time through the vessel imparting a smallimpact is shortened, only a soft shearing force is applied to thesuspension, making it possible to loosen the coagulation of primaryparticles without any influence on the shape and crystallinity of thenegative electrode active material. When the diameter of the beads islarger than 0.45 mmφ, there is a concern that too much energy is appliedto the suspension when the suspension is circulated through the beadsmill, causing easy coagulation among particles in the suspension, on thecontrary. Then, the suspension free from any flock is applied and dried,whereby a negative electrode that satisfies the above conditions (1) to(4) can be produced.

The positive electrode and nonaqueous electrolyte to be used in thenonaqueous electrolyte battery will be explained.

1) Positive Electrode

The positive electrode comprises a positive electrode current collectorand a positive electrode active material-containing layer which issupported on one or both surfaces of the positive electrode currentcollector and containing an active material, a conductive agent and abinder.

This positive electrode is manufactured by adding the conductive agentand the binder to the positive electrode active material, suspending themixture in an appropriate solvent and applying the suspension to acurrent collector such as an aluminum foil, followed by drying andpressing to make a band-shaped material.

Examples of the above positive electrode active material include variousoxides and sulfides. Specific examples of the positive electrode activematerial include manganese dioxide (MnO₂), iron oxide, copper oxide,nickel oxide, lithium-manganese composite oxide such as Li_(x)Mn₂O₄ orLi_(x)MnO₂, lithium-nickel composite oxide such as Li_(x)NiO₂,lithium-cobalt composite oxide such as Li_(x)CoO₂, lithium-nickel-cobaltcomposite oxide, lithium-manganese-cobalt composite oxide,lithium-manganese-nickel composite oxide, spinel-typelithium-manganese-nickel composite oxide such as Li_(x)Mn_(2−y)Ni_(y)O₄,lithium phosphates having an olivine structure, iron sulfate such asFe₂(SO₄)₃ and vanadium oxide such as V₂O₅.

Examples of the lithium-nickel-cobalt composite oxides includeLiNi_(1−y−z)Co_(y)M_(z)O₂ (M is at least one element selected from thegroup consisting of Al, Cr and Fe, 0≦y≦0.5 and 0≦z≦0.1). Examples of thelithium-manganese-cobalt composite oxides includeLiMn_(1−y−z)Co_(y)M_(z)O₂ (M is at least one element selected from thegroup consisting of Al, Cr and Fe, 0≦y≦0.5 and 0≦z≦0.1). Examples of thelithium-manganese-nickel composite oxides includeLiMn_(x)Ni_(x)M_(1−2x)O₂ (M is at least one element selected from thegroup consisting of Co, Cr Al and Fe, 1/3≦x≦1/2). Examples of the oxidesrepresented by LiMn_(x)Ni_(x)M_(1−2x)O₂ includeLiMn_(1/3)Ni_(1/3)Co_(1/3)O₂ and LiMn_(1/2)Ni_(1/2)O₂. Examples oflithium phosphates having an olivine structure include Li_(x)FePO₄,Li_(x)Fe_(1−y)Mn_(y)PO₄ and Li_(x)CoPO₄.

Also, organic materials and inorganic materials including conductivepolymer materials such as polyaniline and polypyrrole, disulfide typepolymer materials, sulfur (S) and carbon fluoride may be used.

In this case, x, y and z the preferable ranges of which are notdescribed above are respectively in the range of 0 to 1.

More preferable examples of the material used for the positive electrodeof secondary batteries include lithium-manganese composite oxides,lithium-nickel composite oxides, lithium-cobalt composite oxides,lithium-nickel-cobalt composite oxides, lithium-manganese-nickelcomposite oxides, spinel type lithium-manganese-nickel composite oxides,lithium-manganese-cobalt composite oxides and lithium-iron-phosphates.These positive electrodes ensure a high battery voltage.

Examples of the above conductive agent may include acetylene black,ketjen black, graphite and cokes.

Examples of the above binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF) and fluorine-type rubbers.

The compounding ratio of the above positive electrode active material,conductive agent and binder is preferably as follows: the positiveelectrode active material: 80 to 95% by weight, the conductive agent: 3to 20% by weight and the binder: 2 to 7% by weight.

It is desirable for the current collector to be formed of an aluminumfoil or an aluminum alloy foil. It is desirable for the aluminum foil orthe aluminum alloy foil forming the current collector to have an averagecrystal grain size not larger than 50 μm. It is more desirable for theaverage crystal grain size noted above to be not larger than 30 μm, andfurthermore desirably not larger than 5 μm. Where the average crystalgrain size of the aluminum foil or the aluminum alloy foil forming thecurrent collector is not larger than 50 μm, the mechanical strength ofthe aluminum foil or the aluminum alloy foil can be drasticallyincreased to make it possible to press the positive electrode with ahigh pressure. It follows that the density of the positive electrode canbe increased to increase the battery capacity.

It is desirable for the aluminum foil or the aluminum alloy foil to havea thickness not larger than 50 μm, preferably not larger than 25 μm.Also, it is desirable for the aluminum foil to have a purity not lowerthan 99%. Further, it is desirable for the aluminum alloy to contain,for example, magnesium, zinc and silicon. On the other hand, it isdesirable for the content of the transition metals such as iron, copper,nickel and chromium in the aluminum alloy to be not higher than 1%.

2) Nonaqueous Electrolyte

This nonaqueous electrolyte contains a nonaqueous solvent and anelectrolyte salt to be dissolved in this nonaqueous solvent. Also, apolymer may be contained in the nonaqueous solvent.

Examples of the electrolyte salt include lithium salts such as LiPF₆,LiBF₄, Li(CF₃SO₂)₂N (bistrifluoromethanesulfonylamide lithium (popularname: LiTFSI)), LiCF₃SO₃ (popular name: LiTFS), Li(C₂F₅SO₂)₂N(bispentafluoroethanesulfonylamide lithium (popular name: LiBETI)),LiClO₄, LiAsF₆, LiSbF₆, lithium bis-oxalatoborate (LiB(C₂O₄)₂ (popularname: LiBOB)) anddifluoro(trifluoro-2-oxide-2-trifluoro-methylpropionate(2-)-0,0) lithiumborate (LiBF₂(OCOOC(CF₃)₂) (popular name: LiBF₂(HHIB))). Theseelectrolyte salts may be used either singly or in combination of two ormore. Particularly, LiPF₆ and LiBF₄ are preferable.

Here, the concentration of the electrolyte salt is preferably in therange of 1.5 to 3M.

Examples of the nonaqueous solvent include, though not particularlylimited to, propylene carbonate (PC), ethylene carbonate (EC),1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF),2-methyltetrahydrofuran (2-MeHF), 1,3-dioxolan, sulfolane, acetonitrile(AN), diethyl carbonate (DEC), dimethyl carbonate (DMC), methylethylcarbonate (MEC) and dipropyl carbonate (DPC). These solvents may be usedeither singly or in combination of two or more. Among these solvents,γ-butyrolactone is preferable. Also, when two or more solvents arecombined, these solvents are all preferably selected from those having adielectric constant of 20 or more.

Additives may be added to this nonaqueous electrolyte. Examples of theseadditives include, though not particularly limited to, vinylenecarbonate (VC), vinylene acetate (VA), vinylene butylate, vinylenehexanate, vinylene crotonate and catechol carbonate. The concentrationof the additives is preferably in the range of 0.1 to 3 wt % withrespect to 100 wt % of the nonaqueous electrolyte. A more preferablerange is 0.5 to 1 wt %.

The structure of the nonaqueous electrolyte battery according to thefirst embodiment is not particularly restricted, and may be variousstructures such as a flat structure, a rectangular structure and acylindrical structure. An example of the flat nonaqueous electrolytebattery is shown in FIGS. 2 to 4.

As shown in FIG. 2, an electrode group 1 has a structure in which apositive electrode 2 and a negative electrode 3 are coiled in a flatshape with interposition of a separator 4 between the electrodes. Theelectrode group 1 is manufactured by applying hot-press after coilingthe positive electrode 2 and negative electrode 3 with interposition ofthe separator 4 therebetween. The positive electrode 2, negativeelectrode 3 and separator 4 in the electrode group 1 may be integratedwith an adhesive polymer. A belt-like positive electrode terminal 5 iselectrically connected to the positive electrode 2, while a belt-likenegative electrode terminal 6 is electrically connected to the negativeelectrode 3. The electrode group 1 is housed in a laminate film case 7having heat-seal portions on three edges as an outer package member. Thetips of the positive electrode terminal 5 and negative electrodeterminal 6 are pulled out from the shorter edge of the heat seal portionof the case 7.

While the tips of the positive electrode terminal 5 and negativeelectrode terminal 6 are pulled out from the same heat seal portion ofthe case 7 as shown in FIG. 2, the heat seal portion from which thepositive electrode terminal 5 is pulled out may be different from theheat seal portion from which the negative electrode terminal 6 is pulledout. A specific example of the structure is shown in FIGS. 3 and 4.

As shown in FIG. 3, a laminated electrode group 8 is housed in the case7 made of the laminate film. As show in FIG. 4, the laminate filmcomprises, for example, a resin layer 10, a thermoplastic resin layer11, and a metal layer 9 disposed between the resin layer 10 andthermoplastic resin layer 11. The thermoplastic resin layer 11 islocated on the inner surface of the case 7. Heat-seal portions 7 a, 7 band 7 c are formed by thermal adhesion of the thermoplastic resin layer11 at one longer edge and both shorter edges of the case 7 made of thelaminate film. The case 7 is sealed with the heat-seal portions 7 a, 7 band 7 c. The laminated electrode group 8 has a structure in which thepositive electrodes 2 and negative electrodes 3 are alternatelylaminated with interposition of the separators 4 between them. Pluralpositive electrodes 2 are used, and each electrode comprises a positiveelectrode current collector 2 a and positive electrode activematerial-containing layers 2 b laminated on both surfaces of thepositive electrode current collector 2 a. Plural negative electrodes 3are used, and each electrode comprises a negative electrode currentcollector 3 a and negative electrode active material-containing layers 3b laminated on both surfaces of the negative electrode current collector3 a. One edge of the negative electrode current collector 3 a of thenegative electrode 3 is protruded out of the positive electrode 2. Thenegative electrode current collector 3 a protruded out of the positiveelectrode 2 is electrically connected to the belt-like negativeelectrode terminal 6. The tip of the belt-like negative electrodeterminal 6 is pulled out to the outside through the heat seal portion 7c of the case 7. Both surfaces of the negative electrode terminal 6 areopposed to the thermoplastic resin layers 11 that constitute the heatseal portion 7 c. An insulation film 12 is inserted between each surfaceof the negative electrode terminal 6 and the thermoplastic resin layer11 for improving the bonding strength between the heat seal portion 7 cand the negative electrode terminal 6. An example of the insulation film12 is a film formed of a material prepared by adding an acid anhydrideto a polyolefin that contains at least one of polypropylene andpolyethylene. The edge of the positive electrode current collector 2 aof the positive electrode 2 is protruded out of the negative electrode3, although this configuration is not illustrated in the drawing. Theedge of the positive electrode current collector 2 a is positioned at anopposed side to the protruded edge of the negative electrode currentcollector 3 a. The positive electrode current collector 2 a protrudedout of the negative electrode 3 is electrically connected to thebelt-like positive electrode terminal 5. The tip of the belt-likepositive electrode terminal 5 is pulled out through the heat sealportion 7 b of the case 7. The insulation film 12 is interposed betweenthe positive electrode terminal 5 and the thermoplastic resin layer 11for improving bonding strength between the heat seal portion 7 b and thepositive electrode terminal 5. The direction in which the positiveelectrode terminal 5 is pulled out of the case 7 is opposed to thedirection in which the negative electrode terminal 6 is pulled out ofthe case 7, as is evident from the above-described construction.

As shown in FIGS. 3 and 4, a nonaqueous electrolyte battery favorablefor use under a large load current may be provided by providing thepull-out direction of the positive electrode terminal 5 so as to beopposed to the pull-out direction of the negative electrode terminal 6.

Examples of the structure of the electrode group include a coilstructure, as shown in FIG. 1 mentioned above, and a laminate structureas shown in FIGS. 3 and 4 mentioned above. In the laminate structure,the separator may be folded in a zigzag shape in use, as shown in FIG.5. A band-shaped separator 4 is folded in a zigzag shape. A negativeelectrode 3 ₁ strip is laminated on the top layer of the separator 4folded in a zigzag shape. A positive electrode 2 ₁ strip, a negativeelectrode 3 ₂ strip, a positive electrode 2 ₂ strip and a negativeelectrode 3 ₃ strip are each inserted in this order from above into apart where the separators 4 are overlapped on each other. The positiveelectrodes 2 and the negative electrodes 3 are alternately arrangedbetween the separators 4 piled in a zigzag shape to thereby obtain anelectrode group having a laminate structure.

The above separator, positive electrode terminal, negative electrodeterminal and outer package member will be explained.

Examples of the material used for the separator may include porous filmscontaining polyethylene, polypropylene, cellulose or polyvinylidenefluoride (PVdF) and synthetic resin nonwoven fabrics. Among thesematerials, porous films made of polyethylene or polypropylene melt at afixed temperature to thereby cut off current and are thereforepreferable in terms of improving safety. Also, nonwoven fabrics made ofcellulose have a high porosity and therefore suppress clogging caused bya resistant component in high-temperature storage.

The positive electrode terminal may be formed from materials havingelectric stability and conductivity in a potential range of 3V to 5Vwith respect to a lithium ion metal. Specific examples of the materialinclude aluminum and aluminum alloys containing elements such as Mg, Ti,Zn, Mn, Fe, Cu and Si. It is preferable to use the same material that isused for the positive electrode current collector to reduce the contactresistance.

The negative electrode terminal may be formed from materials havingelectric stability and conductivity in a potential range of 0.4V to 3Vwith respect to a lithium ion metal. Specific examples of the materialinclude aluminum and aluminum alloys containing elements such as Mg, Ti,Zn, Mn, Fe, Cu and Si. It is preferable to use the same material that isused for the negative electrode current collector to reduce the contactresistance.

A multilayer film comprising a metal foil covered with a resin film maybe used for the laminate film constituting the outer package member. Theresin available includes polymer films such as polypropylene (PP),polyethylene (PE), nylon or polyethylene terephthalate (PET). As shownin FIG. 4 above, polypropylene (PP) or polyethylene (PE) may be used asa thermoplastic resin when one of the resin films is formed of thethermoplastic resin. The metal foil can be formed of aluminum or analuminum alloy. The thickness of the laminate film is desirably 0.2 mmor less.

While the outer package member made of the laminate film is used inFIGS. 2 to 4, the material of the outer package member is notparticularly restricted and, for example, a case made of a metal with athickness of 0.5 mm or less may be used. The metal case available is arectangular or cylindrical metal can made of aluminum, an aluminumalloy, iron or stainless steel. The thickness of the metal case isdesirably 0.2 mm or less.

The aluminum alloy constituting the metal case is preferably an alloycontaining elements such as magnesium, zinc and silicon. However, thecontent of transition metals such as iron, copper, nickel and chromiumis preferably 1% or less. This composition permits long term reliabilityunder a high temperature environment and heat dissipating ability to beremarkably improved.

The metal can made of aluminum or an aluminum alloy preferably has anaverage crystal grain size of 50 μm or less, more preferably 30 μm orless, and further preferably 5 μm or less. The strength of the metal canmade of aluminum or an aluminum alloy can be remarkably increased bycontrolling the average crystal grain size to be 50 μm or less to enablethe can to be thin. Consequently, a vehicle-mounted battery that islight weight, shows high output power and is excellent in long termreliability can be realized.

FIG. 6 shows a nonaqueous electrolyte battery using a metal caseaccording to an embodiment.

The outer package member comprises a case 81 which has a bottomedrectangular cylinder form and is made of aluminum or an aluminum alloy,a lid 82 disposed on an opening part of the case 81 and a negativeelectrode terminal 84 attached to the lid 82 through an insulatingmaterial 83. The case 81 also serves as a positive electrode terminal.As the above aluminum or aluminum alloy constituting the case 81, thosehaving the aforementioned composition and average crystal grain size maybe used.

An electrode group 85 is housed in the case 81. The electrode group 85has a structure in which a positive electrode 86 and a negativeelectrode 87 are coiled through a separator 88 in a flat form. Thiselectrode group 85 is obtained in the following manner: for example, aband-like product obtained by laminating the positive electrode 86, theseparator 88 and the negative electrode 87 in this order is coiled in aspiral form by using a plate or cylindrical core such that the positiveelectrode 86 is positioned on the outside, and the obtained coiledproduct is molded under pressure in the radial direction.

The nonaqueous electrolytic solution (liquid nonaqueous electrolyte) isheld in the electrode group 85. A spacer 90 which is provided with alead-takeoff hole 89 in the vicinity of the center thereof and made of,for example, a synthetic resin is disposed on the electrode group 85 inthe case 81.

A takeoff hole 91 for the negative electrode terminal 84 is opened inthe vicinity of the center of the lid 82. A liquid injection port 92 isformed at a position apart from the takeoff hole 91 of the lid 82. Theliquid injection port 92 is sealed with a seal plug 93 after thenonaqueous electrolytic solution is injected into the case 81. Thenegative electrode terminal 84 is hermetically sealed in the takeoffhole 91 of the lid 82 through a glass or resin insulating material 83.

A negative electrode lead tab 94 is welded to the lower bottom surfaceof the negative electrode terminal 84. The negative electrode lead tab94 is electrically connected to the negative electrode 87. One end of apositive electrode lead 95 is electrically connected to the positiveelectrode 86 and the other end thereof is welded to the lower surface ofthe lid 82. An insulating paper 96 covers the entire outer surface ofthe lid 82. An outer package tube 97 covers the entire side surface ofthe case 81, and the upper and lower ends thereof are folded so as tocover the upper and lower surfaces of the battery body, respectively.

Second Embodiment

A battery pack according to a second embodiment comprises the nonaqueousbattery according to the first embodiment. The number of the nonaqueouselectrolyte batteries may be two or more. It is desirable that thenonaqueous electrolyte battery according to the first embodiment be usedas a unit cell and each unit cell be arranged electrically in series orin parallel to constitute a battery module.

The nonaqueous electrolyte battery according to the first embodiment issuitable for use as a battery module and the battery pack according tothe second embodiment is superior in output performance and cycleperformance. The reason will be explained.

When the negative electrode is improved in nonaqueous electrolyteimpregnation ability and in the uniformity of the distribution of thenegative electrode active material, overvoltage is scarcely applied tothe negative electrode. As a result, the negative electrode can beprevented from falling into a local overcharge or overdischarge stateand it is therefore possible to equalize the utilization factor of thenegative electrode active material. This makes it possible to greatlyreduce differences in capacity and impedance between unit cellsconstituting the battery module. Specifically, in the battery moduleobtained by connecting unit cells in series, a variation in voltagebetween unit cells in a fully charged state is reduced because anydifference in capacities of the unit cells becomes small. Therefore, thebattery pack according to the second embodiment is superior in outputperformance and can be improved in cycle performance.

Each of a plurality of unit cells 21 included in the battery pack shownin FIG. 7 is formed of, though not limited to, a flattened typenonaqueous electrolyte battery constructed as shown in FIG. 2. It ispossible to use the flattened type nonaqueous electrolyte battery shownin FIGS. 3 and 6 as the unit cell 21. The plural unit cells 21 arestacked one upon the other in the thickness direction in a manner toalign the protruding directions of the positive electrode terminals 5and the negative electrode terminals 6. As shown in FIG. 8, the unitcells 21 are connected in series to form a battery module 22. The unitcells 21 forming the battery module 22 are made integral by using anadhesive tape 23 as shown in FIG. 7.

A printed wiring board 24 is arranged on the side surface of the batterymodule 22 toward which protrude the positive electrode terminals 5 andthe negative electrode terminals 6. As shown in FIG. 8, a thermistor 25,a protective circuit 26 and a terminal 27 for current supply to theexternal equipment are connected to the printed wiring board 24.

As shown in FIGS. 7 and 8, a wiring 28 on the side of the positiveelectrodes of the battery module 22 is electrically connected to aconnector 29 on the side of the positive electrode of the protectivecircuit 26 mounted to the printed wiring board 24. On the other hand, awiring 30 on the side of the negative electrodes of the battery module22 is electrically connected to a connector 31 on the side of thenegative electrode of the protective circuit 26 mounted to the printedwiring board 24.

The thermistor 25 detects the temperature of the unit cell 21 andtransmits the detection signal to the protective circuit 26. Theprotective circuit 26 is capable of breaking a wiring 31 a on thepositive side and a wiring 31 b on the negative side, the wirings 31 aand 31 b being stretched between the protective circuit 26 and theterminal 27 for current supply to the external equipment. These wirings31 a and 31 b are broken by the protective circuit 26 under prescribedconditions including, for example, the conditions that the temperaturedetected by the thermistor is higher than a prescribed temperature, andthat the over-charging, over-discharging and over-current of the unitcell 21 have been detected. The detecting method is applied to the unitcells 21 or to the battery module 22. In the case of applying thedetecting method to each of the unit cells 21, it is possible to detectthe battery voltage, the positive electrode potential or the negativeelectrode potential. On the other hand, where the positive electrodepotential or the negative electrode potential is detected, lithium metalelectrodes used as reference electrodes are inserted into the unit cells21.

In the case of FIG. 8, a wiring 32 is connected to each of the unitcells 21 for detecting the voltage, and the detection signal istransmitted through these wirings 32 to the protective circuit 26.

Protective sheets 33 each formed of rubber or resin are arranged on thethree of the four sides of the battery module 22, though the protectivesheet 33 is not arranged on the side toward which protrude the positiveelectrode terminals 5 and the negative electrode terminals 6. Aprotective block 34 formed of rubber or resin is arranged in theclearance between the side surface of the battery module 22 and theprinted wiring board 24.

The battery module 22 is housed in a container 35 together with each ofthe protective sheets 33, the protective block 34 and the printed wiringboard 24. To be more specific, the protective sheets 33 are arrangedinside the two long sides of the container 35 and inside one short sideof the container 35. On the other hand, the printed wiring board 24 isarranged along that short side of the container 35 which is opposite tothe short side along which one of the protective sheets 33 is arranged.The battery module 22 is positioned within the space surrounded by thethree protective sheets 33 and the printed wiring board 24. Further, alid 36 is mounted to close the upper open edge of the container 35.

Incidentally, it is possible to use a thermally shrinkable tube in placeof the adhesive tape 23 for fixing the battery module 22. In this case,the protective sheets 33 are arranged on both sides of the batterymodule 22 and, after the thermally shrinkable tube is wound about theprotective sheets, the tube is thermally shrunk to fix the batterymodule 22.

The unit cells 21 shown in FIGS. 7 and 8 are connected in series.However, it is also possible to connect the unit cells 21 in parallel toincrease the cell capacity. Of course, it is possible to connect thebattery packs in series and in parallel.

Also, the embodiments of the battery pack can be changed appropriatelydepending on the use of the battery pack.

The battery pack according to the second embodiment is preferably usedwhen good cycle performance is required at a large load current (highcurrent density). Specifically, the battery pack is used for powersources of digital cameras, vehicle-mounted batteries for two-wheel orfour-wheel hybrid electric cars, two-wheel or four-wheel electric carsand electric mopeds, and power sources of rechargeable vacuum cleaners.

Third Embodiment

The vehicle according to the third embodiment comprises the battery packaccording to the second embodiment. The vehicle as used herein includestwo- to four-wheel hybrid electric cars, from two- to four-wheelelectric cars, and motor-assisted bicycles.

FIGS. 9 to 11 show various type of hybrid vehicles in which an internalcombustion engine and a motor driven by a battery pack are used incombination as the power source for the driving. The hybrid vehicle canbe roughly classified into three types depending on the combination ofthe internal combustion engine and the electric motor.

FIG. 9 shows a hybrid vehicle 50 that is generally called a serieshybrid vehicle. The motive power of an internal combustion engine 51 isonce converted entirely into an electric power by a power generator 52,and the electric power thus converted is stored in a battery pack 54 viaan inverter 53. The battery pack according to the second embodiment isused as the battery pack 54. The electric power stored in the batterypack 54 is supplied to an electric motor 55 via the inverter 53, withthe result that wheels 56 are driven by the electric motor 55. In otherwords, the hybrid vehicle 50 shown in FIG. 9 represents a system inwhich a power generator is incorporated into an electric vehicle. Theinternal combustion engine can be operated under highly efficientconditions and the kinetic energy of the internal combustion engine canbe recovered as the electric power. On the other hand, the wheels aredriven by the electric motor alone and, thus, the hybrid vehicle 50requires an electric motor of a high output. It is also necessary to usea battery pack having a relatively large capacity. It is desirable forthe rated capacity of the battery pack to fall within a range of 5 to 50Ah, more desirably 10 to 20 Ah. Incidentally, the rated capacity notedabove is the capacity at the time when the battery pack is discharged ata rate of 0.2 C.

FIG. 10 shows the construction of a hybrid vehicle 57 that is called aparallel hybrid vehicle. A reference numeral 58 shown in FIG. 10 denotesan electric motor that also acts as a power generator. The internalcombustion engine 51 drives mainly the wheels 56. The motive power ofthe internal combustion engine 51 is converted in some cases into anelectric power by the power generator 58, and the battery pack 54 ischarged by the electric power produced from the power generator 58. Inthe starting stage or the accelerating stage at which the load isincreased, the driving force is supplemented by the electric motor 58.The hybrid vehicle 57 shown in FIG. 10 represents a system based on theordinary vehicle. In this system, the fluctuation in the load of theinternal combustion engine 51 is suppressed so as to improve theefficiency, and the regenerative power is also obtained. Since thewheels 56 are driven mainly by the internal combustion engine 51, theoutput of the electric motor 58 can be determined arbitrarily dependingon the required ratio of the assistance. The system can be constructedeven in the case of using a relatively small electric motor 58 and arelatively small battery pack 54. The rated capacity of the battery packcan be set to fall within a range of 1 to 20 Ah, more desirably 3 to 10Ah.

FIG. 11 shows the construction of a hybrid vehicle 59 that is called aseries-parallel hybrid vehicle, which utilizes in combination both theseries type system and the parallel type system. A power dividingmechanism 60 included in the hybrid vehicle 59 divides the output of theinternal combustion engine 51 into the energy for the power generationand the energy for the wheel driving. The series-parallel hybrid vehicle59 permits controlling the load of the engine more finely than theparallel hybrid vehicle so as to improve the energy efficiency.

It is desirable for the rated capacity of the battery pack to fallwithin a range of 1 to 20 Ah, more desirably 3 to 10 Ah.

It is desirable for the nominal voltage of the battery pack included inthe hybrid vehicles as shown in FIGS. 9 to 11 to fall within a range of200 to 600V.

It is desirable for the battery pack 54 to be arranged in general in thesite where the battery pack 54 is unlikely to be affected by the changein the temperature of the outer atmosphere and unlikely to receive animpact in the event of a collision. In, for example, a sedan typeautomobile shown in FIG. 12, the battery pack 54 can be arranged withina trunk room rearward of a rear seat 61. The battery pack 54 can also bearranged below or behind the rear seat 61. Where the battery has a largeweight, it is desirable to arrange the battery pack 54 below the seat orbelow the floor in order to lower the center of gravity of theautomobile.

An electric vehicle (EV) is driven by the energy stored in the batterypack that is charged by the electric power supplied from outside thevehicle. Since all the power required for the driving of the vehicle isproduced by an electric motor, it is necessary to use an electric motorof a high output. In general, it is necessary to store all the energyrequired for one driving in the battery pack by one charging. It followsthat it is necessary to use a battery pack having a very large capacity.It is desirable for the rated capacity of the battery pack to fallwithin a range of 100 to 500 Ah, more desirably 200 to 400 Ah.

The weight of the battery pack occupies a large ratio of the weight ofthe vehicle. Therefore, it is desirable for the battery pack to bearranged in a low position that is not markedly apart from the center ofgravity of the vehicle. For example, it is desirable for the batterypack to be arranged below the floor of the vehicle. In order to allowthe battery pack to be charged in a short time with a large amount ofthe electric power required for the one driving, it is necessary to usea charger of a large capacity and a charging cable. Therefore, it isdesirable for the electric vehicle to be equipped with a chargingconnector connecting the charger and the charging cable. A connectorutilizing the electric contact can be used as the charging connector. Itis also possible to use a non-contact type charging connector utilizingthe inductive coupling.

FIG. 13 exemplifies the construction of a hybrid motor bicycle 63. It ispossible to construct a hybrid motor bicycle 63 exhibiting a high energyefficiency and equipped with an internal combustion engine 64, anelectric motor 65, and the battery pack 54 like the hybrid vehicle. Theinternal combustion engine 64 drives mainly the wheels 66. In somecases, the battery pack 54 is charged by utilizing a part of the motivepower generated from the internal combustion engine 64. In the startingstage or the accelerating stage in which the load of the motor bicycleis increased, the driving force of the motor bicycle is supplemented bythe electric motor 65. Since the wheels 66 are driven mainly by theinternal combustion engine 64, the output of the electric motor 65 canbe determined arbitrarily based on the required ratio of the supplement.The electric motor 65 and the battery pack 54, which are relativelysmall, can be used for constructing the system. It is desirable for therated capacity of the battery pack to fall within a range of 1 to 20 Ah,more desirably 3 to 10 Ah.

FIG. 14 exemplifies the construction of an electric motor bicycle 67.The electric motor bicycle 67 is driven by the energy stored in thebattery pack 54 that is charged by the supply of the electric power fromthe outside. Since all the driving force required for the driving themotor bicycle 67 is generated from the electric motor 65, it isnecessary to use the electric motor 65 of a high output. Also, since itis necessary for the battery pack to store all the energy required forone driving by one charging, it is necessary to use a battery packhaving a relatively large capacity. It is desirable for the ratedcapacity of the battery pack to fall within a range of 10 to 50 Ah, moredesirably 15 to 30 Ah.

Fourth Embodiment

FIGS. 15 and 16 show an example of a rechargeable vacuum cleaneraccording to a fourth embodiment. The rechargeable vacuum cleanercomprises an operating panel 75 which selects operation modes, anelectrically driven blower 74 comprising a fun motor for generatingsuction power for dust collection, and a control circuit 73. A batterypack 72 according to the second embodiment as a power source for drivingthese units are housed in a casing 70. When the battery pack is housedin such a portable device, the battery pack is desirably fixed withinterposition of a buffer material in order to prevent the battery packfrom being affected by vibration. Known technologies may be applied formaintaining the battery pack at an appropriate temperature. While abattery charger 71 that also serves as a setting table functions as thebattery charger of the battery pack according to the second embodiment,a part or all of the function of the battery charger may be housed inthe casing 70.

While the rechargeable vacuum cleaner consumes a large electric power,the rated capacity of the battery pack is desirably in the range of 2 to10 Ah, more preferably 2 to 4 Ah, in terms of portability and operationtime. The nominal voltage of the battery pack is desirably in the rangeof 40 to 80V.

The present invention will be explained in detail by way of exampleswith reference to the drawings.

Example 1 Production of a Positive Electrode

LiCoO₂ was used as a positive electrode active material, to which wereadded a graphite powder as a conductive agent in an amount of 8% byweight based on the total amount of the positive electrode and PVdF as abinder in an amount of 5% by weight based on the total amount of thepositive electrode. These components were dispersed in ann-methylpyrrolidone (NMP) solvent to prepare a slurry. The obtainedslurry was applied to a 15-μm-thick aluminum foil, which was thentreated through drying and pressing processes to manufacture a positiveelectrode having an electrode density of 3.3 g/cm³.

<Production of a Negative Electrode>

Li₄Ti₅O₁₂ particles having a spinel structure and an average particlediameter of 0.9 μm were prepared as a negative electrode activematerial. To this negative electrode active material were added graphiteas a conductive agent in an amount of 10% by weight based on the totalamount of the negative electrode, and PVdF as a binder in an amount of3% by weight based on the total amount of the negative electrode. Thesecomponents were dispersed in an n-methylpyrrolidone (NMP) solvent toprepare a slurry. The slurry was kneaded at 5° C. for 18 hours.Furthermore, the kneaded slurry was subjected to a beads mill processwith a 1.7 L vessel to carry out circulation operation at a flow rate of3 L/min for 30 minutes. When the capacity of the vessel is A (L), theflow rate corresponds to 1.8 A (L). At this time, 0.3 mmφ zirconia beadswere used. When the slurry as the product to be treated is made to passthrough the beads mill using small-diameter beads at a large flow rate,that is, when the retention time during which the slurry is made to passone time through the vessel imparting a small impact is shortened, onlya soft shearing force is applied to the slurry, making it possible toloosen the coagulation of primary particles without any influence on theshape and crystallinity of the Li₄Ti₅O₁₂ particles. Then, the obtainedslurry was applied to a current collector made of an aluminum foil 15 μmin thickness and dried, followed by pressing, to produce a negativeelectrode having an electrode density of 2.1 g/cm³.

The distribution of pore size diameter of the obtained negativeelectrode was measured by mercury porosimetry and as a result, thespecific surface area of pores calculated based on the weight of thenegative electrode, excluding the weight of the negative electrodecurrent collector, was 8.7 m²/g. The total pore volume per 1 g of thenegative electrode excluding the negative electrode current collectorwas 0.1521 mL/g. The volume of pores having a diameter of 0.05 μm orless per 1 g of the negative electrode excluding the negative electrodecurrent collector was 0.033 mL/g. Accordingly, the ratio of the volumeof pores having a pore size diameter of 0.05 μm or less to the totalpore volume was 21.70%. Also, the log differential intrusion curve had apeak at a pore size diameter of 0.085 μm. Also, the above curveattenuated with a decrease in pore size diameter from the apex presentat a pore size diameter of 0.085 μm.

<Preparation of a Nonaqueous Electrolyte>

2M of LiBF₄ was mixed in a mixture solvent prepared by blending EC, PCand GBL in a ratio by volume of 1:1:4 to make a nonaqueous electrolyte.

<Fabrication of a Battery>

A separator made of a polyethylene porous film was impregnated with thenonaqueous electrolyte. The positive electrode was coated with thisseparator. The negative electrode was overlapped on the positiveelectrode with the separator therebetween, and the electrodes andseparator were coiled into a spiral form to manufacture a spiralelectrode group. This electrode group was pressed into a flat form. Theflattened electrode group was inserted into a can-shaped case made ofaluminum 0.3 mm in thickness to manufacture a 3.0-mm-thick, 35-mm-wideand 62-mm-high flat-type nonaqueous electrolyte battery shown in FIG. 6.

After the obtained battery was charged up to 50% of the rated value, itwas discharged under 1 C for 10 seconds. Thereafter, the battery wasrecharged up to 50% of the rated value and then, it was discharged under5 C for 10 seconds. The current value when the voltage of the batteryreached 1.5V was found from the cutoff voltage in the 1 C dischargeoperation and from the cutoff voltage in the 5 C discharge operation byextrapolation. The power calculated from the current value at 1.5V, thatis, the maximum power among powers applied for 10 seconds was 150 W.

The log differential intrusion curve and cumulative pore intrusioncurve, which showed the pore size diameter distribution of the negativeelectrode measured by mercury porosimetry, were measured using themethods described below.

An Autopore 9520 model, manufactured by Shimadzu Corporation, was usedas the measuring device. The negative electrode was cut into a size of25×25 mm² to prepare a sample, which was then folded and placed in ameasuring cell for measurement under the condition of an initialpressure of 20 kPa which corresponds to about 3 psia and also to apressure applied to a sample having a pore size diameter of about 60 μm.An average of three samples was used as the result of measurement. Inthe adjustment of data, the specific surface area of pores wascalculated on the premise that the pore had a cylindrical form. When theapex of a peak was present in a pore size diameter range of 0.03 μm to0.2 μm in the log differential intrusion curve, the presence of the peakin this range was recognized.

It should be noted that the analytical principle of the mercuryporosimetry is based on Washburn's equation (B):D=−4γ cos θ/P  Equation (B)

Here, P is a pressure to be applied, D is a pore size diameter, γ is thesurface tension of mercury and is 480 dyne·cm⁻¹, and θ is a contactangle of mercury with the wall surface of pores and is 140°. γ and θ areconstants and therefore, the relation between the applied pressure P andthe pore size diameter D is found from Washburn's equation. If mercurypenetration volume at this time is measured, the pore size diameter andits volumetric distribution can be found. As to the details of measuringmethod, principle and the like, please refer to, for example, MotojiZimpo et al., “Microparticle Handbook” Asakura Shoten, (1991) andSohachiro Hayakawa, “Powder Property Measuring Method”, Asakura Shoten(1978).

Examples 2 to 9 and Comparative Example 1

A battery was manufactured in the same manner as in Example 1 exceptthat the flow rate when the negative electrode slurry was circulated andthe diameter of the beads were altered to those shown in the followingTable 1 and a negative electrode was used which had the value shown inTable 1 as the result of measurement using mercury porosimetry.

Example 10

A battery was produced in the same manner as in Example 1 except thatLi₂Ti₃O₇ particles having an average particle diameter of 0.5 μm wereused as the negative electrode active material.

Comparative Example 2

To the same negative electrode active material explained in Example 1was added graphite as a conductive agent in an amount of 10% by weightbased on the total amount of the negative electrode, and PVdF as abinder in an amount of 3% by weight based on the total amount of thenegative electrode. These components were dispersed in ann-methylpyrrolidone (NMP) solvent to prepare a slurry. The slurry waskneaded and then, the kneaded slurry was subjected to a beads millprocess using zirconia beads having a diameter of 1 mmφ to retain theslurry there for 60 minutes, thereby applying a sufficient load on theslurry to disperse the slurry. Then, the obtained slurry was applied toa current collector made of an aluminum foil of 15 μm in thickness anddried, followed by pressing, to produce a negative electrode having anelectrode density of 2.1 g/cm³.

The pore size diameter distribution of the obtained negative electrodewas measured by mercury porosimetry and as a result, the specificsurface area of pores was 7.5 m²/g. The total pore volume was 0.1734mL/g. The volume of pores having a diameter of 0.05 μm or less was 0.021mL/g. Also, the log differential intrusion curve had a peak at a poresize diameter of 0.083 μm. Also, the value of the log differentialintrusion decreased with a decrease in pore size diameter from the apexpresent at a pore size diameter of 0.083 μm, but began increasing at apore size diameter of 0.02 μm to confirm a small peak having an apex ata pore size diameter of 0.014 μm.

The power of each battery is shown in Table 1.

TABLE 1 Volume (B) of Peak top pores having a Residence pore Specificpore size Diameter time in the size surface area Total pore diameterRatio of Flow rate of beads beads mill diameter of pores volume (A) of0.05 μm or B to A Power (L/min) (μm) (min) (μm) (m²/g) (mL/g) less(mL/g) (%) value (W) Example 1 3(1.8A) 0.3 30 0.085 8.7 0.1521 0.03321.70 150 Example 2 3(1.8A) 0.3 30 0.071 25.0 0.2234 0.0814 36.44 180Example 3 3(1.8A) 0.3 30 0.055 100.0 0.4812 0.1753 36.43 230 Example 43(1.8A) 0.3 30 0.081 8.5 0.1000 0.0397 39.70 130 Example 5 3(1.8A) 0.330 0.080 9.1 0.5000 0.1550 31.00 170 Example 6 3(1.8A) 0.3 30 0.03 95.00.4283 0.3776 88.16 380 Example 7 3(1.8A) 0.3 30 0.2 6.2 0.1208 0.02520.70 110 Example 8 3(1.8A) 0.3 30 0.102 6.0 0.1355 0.028 20.66 120Example 9 3(1.8A) 0.3 30 0.085 8.6 0.1520 0.0304 20 130 Example 103(1.8A) 0.3 30 0.072 12.5 0.1933 0.064 33.11 175 Comparative 0.2(0.12A) 0.5 30 0.084 8.3 0.1633 0.0210 12.86 75 Example 1 Comparative — 1 600.083 7.5 0.1734 0.021 12.11 95 Example 2

As is clear from Table 1, it is understood that each battery obtained inExamples 1 to 10 using a negative electrode satisfying the aboveconditions (1) to (4) is increased in the maximum power obtained byoutputting power for 10 seconds over that of each battery obtained inComparative Examples 1 and 2. The battery of Comparative Example 1 failsto fulfill the condition (3). Since the ratio of the volume of poreshaving a pore size diameter of 0.05 μm or less to the total pore volumewas less than 20%, the maximum power was low. Also, in the case of thenegative electrode obtained in Comparative Example 2, the diameter ofthe beads was increased to stir the slurry strongly and therefore, thesurface of primary particles of Li₄Ti₅O₁₂ was scraped, with the resultthat a second peak appeared at a pore size diameter smaller than that atwhich the apex of the peak was present in the log differential intrusioncurve. Also, the ratio of the volume of pores having a pore sizediameter of 0.05 μm or less to the total pore volume was less than 20%.Such a negative electrode was inferior in the uniformity of thedistribution of the negative electrode active material and was thereforereduced in the maximum power.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A nonaqueous electrolyte battery comprising: a positive electrode; anegative electrode containing a negative electrode activematerial-containing layer which contains a lithium compound as anegative electrode active material, a binder and a conductor, and anegative electrode current collector supporting the negative electrodeactive material-containing layer; and a nonaqueous electrolyte, whereina log differential intrusion curve obtained when a pore size diameter ofthe negative electrode is measured by mercury porosimetry has an apex ofpeak in a pore size diameter range of 0.03 to 0.2 μm and does not havethe apex of peak in a pore size diameter range of less than 0.03 μm, aspecific surface area (excluding a weight of the negative electrodecurrent collector) of pores of the negative electrode found by mercuryporosimetry is 6 to 100 m²/g, and a ratio of a volume of pores having apore size diameter of 0.05 μm or less to a total pore volume is 20% ormore.
 2. The nonaqueous electrolyte battery according to claim 1,wherein a volume of pores measured by the mercury porosimetry is 0.1 to0.5 mL per 1 g of the negative electrode, excluding the negativeelectrode current collector.
 3. The nonaqueous electrolyte batteryaccording to claim 1, wherein the lithium compound includeslithium-titanium oxide.
 4. The nonaqueous electrolyte battery accordingto claim 3, wherein the lithium-titanium oxide has a spinel structure ora ramsdellite structure.
 5. The nonaqueous electrolyte battery accordingto claim 1, wherein the apex of peak exists in a pore size diameterrange of 0.04 to 0.1 μm.
 6. The nonaqueous electrolyte battery accordingto claim 1, wherein the ratio is 20 to 90%.
 7. A battery pack comprisinga nonaqueous electrolyte battery, the nonaqueous electrolyte batterycomprising: a positive electrode; a negative electrode containing anegative electrode active material-containing layer which contains alithium compound as a negative electrode active material, a binder, anda conductor, and a negative electrode current collector supporting thenegative electrode active material-containing layer; and a nonaqueouselectrolyte, wherein a log differential intrusion curve obtained when apore size diameter of the negative electrode is measured by mercuryporosimetry has a peak in a pore size diameter range of 0.03 to 0.2 μmand does not have the apex of peak in a pore size diameter range of lessthan 0.03 μm, a specific surface area (excluding a weight of thenegative electrode current collector) of pores of the negative electrodefound by mercury porosimetry is 6 to 100 m2/g, and a ratio of a volumeof pores having a pore size diameter of 0.05 μm or less to a total porevolume is 20% or more.
 8. The battery pack according to claim 7, whereina volume of pores measured by mercury porosimetry is 0.1 to 0.5 mL per 1g of the negative electrode, excluding the negative electrode currentcollector.
 9. The battery pack according to claim 7, wherein the lithiumcompound includes lithium-titanium oxide.
 10. The battery pack accordingto claim 9, wherein the lithium-titanium oxide has a spinel structure ora ramsdellite structure.
 11. The battery pack according to claim 7,wherein the apex of peak exists in a pore size diameter range of 0.04 to0.1 μm.
 12. The battery pack according to claim 7, wherein the ratio is20 to 90%.
 13. A vehicle comprising: a nonaqueous electrolyte batteryincluding, a positive electrode, a negative electrode containing anegative electrode active material-containing layer which contains alithium compound as a negative electrode active material, a binder and aconductor, and a negative electrode current collector supporting thenegative electrode active material-containing layer; and a nonaqueouselectrolyte, wherein a log differential intrusion curve obtained when apore size diameter of the negative electrode is measured by mercuryporosimetry has an apex of peak in a pore size diameter range of 0.03 to0.2 μm and does not have the apex of peak in a pore size diameter rangeof less than 0.03 μm, a specific surface area (excluding a weight of thenegative electrode current collector) of pores of the negative electrodefound by mercury porosimetry is 6 to 100 m²/g, and a ratio of a volumeof pores having a pore size diameter of 0.05 μm or less to a total porevolume is 20% or more.